Measurement of blood volume using Fourier-transform based velocity-selective pulse trains on MRI

Abstract

The present invention is directed to a system and method for determining blood volume in a subject. Blood volume is an important hemodynamic parameter for monitoring many disorders, such as stoke and cancer. Current MRI techniques for quantification of absolute blood volume for such clinical applications all require injecting exogenous contrast agents. To reduce associated safety risks and cost, the present invention is directed to a non-contrast-enhanced MRI method for blood volume mapping on MRI. The technique of the present invention employs velocity-selective (VS) pulse trains in paired control and label modules for separating vascular signal by subtraction. The Fourier-transform based VS saturation pulse train (FT-VSS) of the present invention has improved performance over conventional VS pulse trains for the blood volume measurement.

What is claimed is: 
     
       1. A method for determining blood volume for a subject comprising:
 performing a Fourier-transform velocity-selective saturation (FT-VSS) pulse train with a magnetic resonance imaging scanner, wherein the FT-VSS pulse train is a concatenated series of small-flip-angle RF pulses interleaved with velocity-encoding gradients, and wherein the FT-VSS pulse train is configured for FT-VSS labeling modules to saturate static tissue while preserving spins flowing above a cutoff velocity (Vc), while the FT-VSS labeling modules apply saturation universally on all spins; 
 embedding refocusing pulses between FT-VSS pulse trains; 
 cancelling out a signal from static tissue; 
 performing a pair of acquisitions with the magnetic resonance imaging scanner; and 
 determining the blood volume for the subject from a difference signal that results from a flowing blood compartment above the Vc, after the signal from the static tissue is cancelled out. 
 
     
     
       2. The method of  claim 1  further comprising using refocusing pulses comprising adiabatic pulses or composite pulses. 
     
     
       3. The method of  claim 1  further comprising using a velocity-sensitized labeling module comprising ±90° pulses. 
     
     
       4. The method of  claim 1  further comprising using alternating velocity-encoding gradients. 
     
     
       5. The method of  claim 1  further comprising leaving a gap between a gradient lobe and an RF pulse of the FT-VSS pulse train to minimize the effect of eddy currents. 
     
     
       6. The method of  claim 1  further comprising generating a non-contrast-enhanced MRI map of blood volume. 
     
     
       7. The method of  claim 1  further comprising using the FT-VSS pulse trains in paired control and label modules for separating vascular signal by subtraction. 
     
     
       8. The method of  claim 1  further comprising leveraging a subtraction-based method using the pair of acquisitions immediately following velocity-sensitized pulse trains for a label module and its corresponding control module, respectively. 
     
     
       9. The method of  claim 1  further comprising cancelling out a signal of static tissue and a resulting difference signal comes from the flowing blood compartment above a cutoff velocity. 
     
     
       10. The method of  claim 1  further comprising normalizing to a proton density-weighted image acquired separately and scaled with blood T1 and T2 relaxation factors and obtaining a quantitative measurement of blood volume. 
     
     
       11. A system for determining blood volume for a subject comprising:
 a magnetic resonance imager; and 
 a non-transitory computer readable medium programmed for: 
 performing a Fourier-transform velocity-selective saturation (FT-VSS) pulse train with the magnetic resonance imager, wherein the FT-VSS pulse train is a concatenated series of small-flip-angle RF pulses interleaved with velocity-encoding gradients, and wherein the FT-VSS pulse train is configured for FT-VSS labeling modules to saturate static tissue while preserving spins flowing above a cutoff velocity (Vc), while the FT-VSS labeling modules apply saturation universally on all spins; 
 embedding refocusing pulses between FT-VSS pulse trains; 
 cancelling out a signal from static tissue; 
 performing a pair of acquisitions with the magnetic resonance imager; and 
 determining the blood volume for the subject from a difference signal that results from a flowing blood compartment above the Vc, after the signal from the static tissue is cancelled out. 
 
     
     
       12. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for using refocusing pulses comprising adiabatic pulses or composite pulses. 
     
     
       13. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for using a velocity-sensitized labeling module comprising ±90° pulses. 
     
     
       14. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for using alternating velocity-encoding gradients. 
     
     
       15. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for leaving a gap between a gradient lobe and an RF pulse of the FT-VSS pulse train to minimize the effect of eddy currents. 
     
     
       16. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for generating a non-contrast-enhanced MRI map of blood volume. 
     
     
       17. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for using the FT-VSS pulse trains in paired control and label modules for separating vascular signal by subtraction. 
     
     
       18. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for leveraging a subtraction-based method using the pair of acquisitions immediately following velocity-sensitized pulse trains for a label module and its corresponding control module, respectively. 
     
     
       19. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for cancelling out a signal of static tissue and a resulting difference signal comes from the flowing blood compartment above a cutoff velocity. 
     
     
       20. The system of  claim 11  further comprising the non-transitory computer readable medium being programmed for normalizing to a proton density-weighted image acquired separately and scaled with blood T1 and T2 relaxation factors and obtaining a quantitative measurement of blood volume.